Obstetric and gynecologic ultrasound curriculum and competency assessment in residency training programs: consensus report.

Ultrasound imaging has become integral to the practice of obstetrics and gynecology. With increasing educational demands and limited hours in residency programs, dedicated time for training and achieving competency in ultrasound has diminished substantially. The American Institute of Ultrasound in Medicine assembled a multi-Society Task Force to develop a consensus-based, standardized curriculum and competency assessment tools for obstetric and gynecologic ultrasound training in residency programs. The curriculum and competency-assessment tools were developed based on existing national and international guidelines for the performance of obstetric and gynecologic ultrasound examinations and thus are intended to represent the minimum requirement for such training. By expert consensus, the curriculum was developed for each year of training, criteria for each competency assessment image were generated, the pass score was established at or close to 75% for each, and obtaining a set of five ultrasound images with pass score in each was deemed necessary for attaining each competency. Given the current lack of substantial data on competency assessment in ultrasound training, the Task Force expects that the criteria set forth in this document will evolve with time. The Task Force also encourages use of ultrasound simulation in residency training and expects that simulation will play a significant part in the curriculum and the competency-assessment process. Incorporating this training curriculum and the competency-assessment tools may promote consistency in training and competency assessment, thus enhancing the performance and diagnostic accuracy of ultrasound examination in obstetrics and gynecology. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Outcome of pregnancies in women with uterine leiomyomas identified by sonography in the first trimester.

PURPOSE: We assessed the outcome of pregnancies in women with uterine leiomyomas (fibroids) documented by sonography in the first trimester of pregnancy. METHODS: We collected cases of women who had undergone first-trimester sonography and had uterine fibroids and singleton pregnancies with documented fetal heartbeats. We compared pregnancy loss rates and modes of delivery in these cases to a maternal-age-matched and gestational-age-matched control group of women who had normal uteruses and first-trimester pregnancies with documented fetal heartbeats. Sonograms in patients with fibroids were reviewed to determine the number of fibroids, their sizes, and their locations. Within the group of patients with fibroids, the pregnancy loss rate was also compared based on the number of fibroids and fibroid size and location. RESULTS: Our study population consisted of 143 women with leiomyomas, and our control group comprised 715 patients with a normal uterus. Among patients with fibroids, 14.7% of pregnancies resulted from assisted conception; in the control group, 6.4% of pregnancies resulted from assisted conception. The rate of spontaneous pregnancy loss in women with fibroids was almost twice the rate in women with normal uteruses (14.0% versus 7.6%; p < 0.05), and the loss rate was higher in women with multiple fibroids than in women with a single leiomyoma (23.6% versus 8.0%, p < 0.05). The loss rate was not significantly associated with fibroid size or location. The rate of cesarean-section delivery was higher in patients with fibroids than in patients with normal uteruses (38% versus 28%, p < 0.05). CONCLUSIONS: Uterine fibroids are associated with an elevated risk of spontaneous pregnancy loss. The loss rate is higher in patients with multiple fibroids than with a single fibroid. The cesarean-section rate is also higher in patients with fibroids than in patients with a normal uterus.

Sonographic and Doppler characteristics of the corpus luteum: can they predict pregnancy outcome?

OBJECTIVE: To determine whether there is a relationship between gray scale or Doppler characteristics of the corpus luteum and first-trimester pregnancy outcome. METHODS: We conducted a prospective study of patients with spontaneous singleton pregnancies between 5 and 8 weeks' gestation. The corpus luteum size, sonographic appearance, resistive index, and peak systolic velocity were measured on transvaginal sonography. Maternal use of exogeneous progesterone was recorded. Only patients with known first-trimester outcome were included. RESULTS: There were 201 study patients. The corpus luteum could be visualized in 197 (98%) and had a mean +/- SD size of 1.9 +/- 0.6 cm, a mean resistive index of 0.50 +/- 0.08, and a peak systolic velocity of 20.5 +/- 11.2 cm/s. There were 151 first-trimester survivors (75.1 %) and 50 spontaneous losses (24.9%). In a comparison of the survivors and losses, there was no significant difference in mean corpus luteum size (1.9 versus 1.7 cm; P = .10, t test), mean resistive index (0.50 versus 0.50; P = .71, t test), peak systolic velocity (21 versus 19 cm/s; P = .29, t test), or sonographic appearance (P = .78, chi2 test). The lack of association between corpus luteum characteristics and outcome persisted when cases were stratified by progesterone use and the presence or absence of a heartbeat on the study sonogram. CONCLUSION: There is no apparent relationship between the characteristics of the corpus luteum and first-trimester pregnancy outcome.

Frequency of a monochorionic pair in multiple gestations: relationship to mode of conception.

OBJECTIVE: To determine whether the mode of conception affects the frequency of monochorionicity in multiple gestations. METHODS: Our study population consisted of all women with multiple gestations who had a first-trimester sonogram at our institution between May 1998 and April 2000. The frequency of monochorionicity in pregnancies conceived naturally was compared with the frequency in pregnancies achieved via any form of assisted reproductive technology and among the different types of assisted reproductive technology. RESULTS: Our study consisted of 464 multiple gestations comprising 332 twin, 113 triplet, 16 quadruplet, and 3 quintuplet pregnancies. The higher the fetal number, the more likely the pregnancy resulted from assisted reproductive technology (72.6% of twins, 84.1% of triplets, 92.8% of quadruplets, and 100% of quintuplets; P < .05, Fisher exact test). Monochorionic pairs were found more commonly in naturally conceived pregnancies than in those resulting from assisted reproductive technology (28.2% versus 5.4%; P < .000001, chi2 test). The frequency of monochorionic pairs after in vitro fertilization with blastocyst transfer on day 5 (10.5%) was double the frequency from in vitro fertilization with cleavage stage transfer on day 3 (4.9%), but the difference was not statistically significant (P = .24, Fisher exact test). CONCLUSIONS: Monochorionic pairs are relatively common in naturally conceived twins and in higher-order multiple gestations with more than 3 fetuses arising from assisted reproductive technology, but they are uncommon in twins and triplets arising from assisted reproductive technology There is a trend toward a higher frequency of monochorionic pairs after day 5 blastocyst transfer than day 3 transfer, but a larger study population is needed to confirm this finding.

Prenatal ultrasonography and the diagnosis of fetal cleft lip.

OBJECTIVE: To determine the efficacy of obstetric ultrasonography in the detection of fetal cleft lip. METHODS: The study population included all women who had a fetal anatomic survey with adequate visualization of the face and who gave birth at Brigham and Women's Hospital between January 1, 1990, and January 31, 2000. All neonates born with cleft lip were identified from the Brigham and Women's Active Malformation Surveillance Program. Confirmation of the anatomic defect was obtained from the pediatric record or from the pathologic report if the pregnancy was terminated or ended in miscarriage. Cases of isolated cleft palate were excluded. An ultrasonography database was used to identify all cases of cleft lip diagnosed before delivery. Maternal information regarding the pregnancy was abstracted from the medical record. Statistical significance was determined using the chi2 statistic for categorical variables and the t test for continuous variables. RESULTS: A total of 56 confirmed cases of cleft lip were identified in the study population. Overall, 73% of the cases (41 of 56) were identified antenatally. Additional fetal anomalies were present in 54% of the cases (30 of 56). A comparison between those cases that were detected and those in which the diagnosis was missed showed that there was a significantly lower detection rate if the ultrasonography was performed before 20 weeks (12 [57%] of 21 versus 29 [83%] of 35; P = .035). There was no difference between the 2 groups in terms of maternal age or weight. Maternal parity, prior maternal abdominal surgery, the presence of a multiple gestation, or coexisting fetal anomalies did not significantly affect the detection rate. There was no difference in detection rate in the first half of the study period (1990-1995; 23 [72%] of 32) compared with the second half (1996-2000; 18 [76%] of 24; P = .79). CONCLUSIONS: In this cohort of women, the rate of detection of fetal cleft lip was significantly lower when the anatomic survey was performed before 20 weeks' gestation. This difference could not be accounted for by such variables as prior maternal abdominal surgery, coexisting fetal anomalies, or improvements in ultrasonographic detection with time. We recommend that the anatomic survey for fetuses at high risk for this condition be performed after 20 weeks' gestation.

Usefulness of ultrasonography in the management of nodular thyroid disease.

BACKGROUND: Fine-needle aspiration biopsy is the standard diagnostic test for evaluating possible malignancy in a thyroid nodule. OBJECTIVE: To evaluate the role of routine ultrasonography in the management of nodular thyroid disease. DESIGN: Retrospective chart review. SETTING: Multidisciplinary thyroid nodule clinic (endocrinology and radiology). PATIENTS: Patients with suspected nodular thyroid disease or suspected recurrent thyroid cancer referred between October 1995 and March 1997. All patients had thyroid ultrasonography and ultrasonography-guided fine-needle aspiration biopsy of nodules at least 1 cm in maximum diameter. MEASUREMENTS: Medical records, ultrasonography findings, cytology reports, and histologic reports were reviewed. Ultrasonography findings were compared with the referring physician's findings on physical examination. RESULTS: 223 patients were seen in the clinic. A total of 209 fine-needle aspiration biopsies were performed on 156 patients. Among 50 of 114 patients referred for a solitary nodule, ultrasonography detected additional nonpalpable nodules at least 1 cm in diameter in 27 and determined that no nodules required aspiration in 23. Of 59 patients referred for a diffuse goiter or a multinodular gland, ultrasonography detected discrete nodules at least 1 cm in diameter that required aspiration in 39 and determined that aspiration was unnecessary in 20. CONCLUSIONS: Ultrasonography altered the clinical management for 63% of the patients (109 of 173) referred to the thyroid nodule clinic after abnormal results on thyroid physical examination.

Outcome of pregnancies with rapid embryonic heart rates in the early first trimester.

OBJECTIVE: We conducted a study to determine the upper limits of normal embryonic heart rate at or before 7.0 weeks' gestational age and to assess outcome of pregnancies in which the early embryonic heart rate is rapid. SUBJECTS AND METHODS: We recorded embryonic heart rates in 2817 sonograms at or before 7.0 weeks' gestation performed between January 1993 and June 1998. The upper limit of normal heart rate in two gestational age ranges (before 6.3 weeks and 6.3-7.0 weeks) was computed as the average of two values: mean heart rate + 1.96 standard deviations and the rate above which 2.5% of embryos in our population were measured. Pregnancy outcome in cases with rapid embryonic heart rates was compared with pregnancy outcome in a control group with normal rates. RESULTS: The upper limit of normal heart rate was 134 beats per minute before 6.3 weeks' gestation and 154 beats per minute at 6.3-7.0 weeks' gestation. Forty-one embryos had rapid early heart rates and known first-trimester outcome, of which 37 (90.2%) were alive at the end of the first trimester. Pregnancy outcome was available in 33 of the 37 first-trimester survivors (four were lost to follow-up before delivery), and 30 of these 33 (90.9%) were healthy neonates. These short- and long-term outcomes were not significantly different from those of the control group of embryos with normal early heart rates (p > 0.20, Fisher's exact test). CONCLUSION: A rapid early embryonic heart rate is one that is at least 135 beats per minute before 6.3 weeks or at least 155 beats per minute at 6.3-7.0 weeks. Pregnancies in which the embryo has a rapid early heart rate have a good prognosis, with a high likelihood of normal outcome.

US evaluation of the uterus in patients with postmenopausal bleeding: A positive effect on diagnostic decision making.

PURPOSE: To assess the accuracy of hysterosonography (HSG) and its role in diagnostic confidence and therapeutic clinical decision making among referring physicians caring for patients with postmenopausal bleeding (PMB). MATERIALS AND METHODS: One hundred twenty-three patients with PMB underwent transvaginal ultrasonography (US) and HSG. They were examined for cancer, polyp, leiomyoma, and hyperplasia. Physicians assessed the effect of the studies on diagnostic confidence and care, including biopsy, dilation and curettage, hysteroscopy, hormone manipulation, and/or patient reassurance. Abnormality was proved with histopathologic evaluation, and normality, with 6-month follow-up. RESULTS: In 10 patients, HSG was unsuccessful, and in 15, follow-up was incomplete; this left 98 patients. Endometrial polyps were seen in 46 (47%) patients; leiomyoma, in 11 (11%); cancer, in four (4%); hyperplasia, in eight (8%); and normal findings, in 29 (30%). Our calculations yielded a sensitivity of 98% and a specificity of 88%. In 86 (88%) patients, US added certainty to the diagnosis; in 78 (80%), it resulted in a change in patient treatment. CONCLUSION: HSG and transvaginal US in patients with PMB improves diagnostic accuracy, clinical decision making, and the clinician's diagnostic certainty. In patients with benign causes of PMB, the absence of abnormality at HSG and a normal endometrial biopsy result may eliminate the need for further studies.

Long-term prognosis of pregnancies complicated by slow embryonic heart rates in the early first trimester.

Slow embryonic heart rates at gestational age 7 weeks or less are associated with high risk of first trimester death. Our goal was to determine the prognosis for those embryos with slow early heart rates who survive the first trimester. We prospectively recorded embryonic heart rates for all obstetrical sonograms obtained on singleton pregnancies at or before 7.0 weeks' gestation since 1993. We collected information about pregnancy outcome, including date of live birth or in utero death and presence and nature of congenital anomalies. First trimester survival rate was 61.6% among 531 embryos with slow early heart rates (< 100 bpm at < or = 6.2 weeks, < 120 bpm at 6.3 to 7.0 weeks), lower than the survival rate of 91.5% among 1501 embryos with normal heart rates (p < 10(-8), Fisher's exact test). Among 299 pregnancies in which the early heart rate was slow and the fetus was still alive at the end of the first trimester, 277 (92.6%) resulted in liveborn infants without congenital anomalies, similar to the frequency of 95.1% in cases with normal early heart rates (p > 0.10, Fisher's exact test). Structural and chromosomal anomalies, however, occurred more than twice as frequently in cases with slow early heart rates: 5.4% (16 of 299) of the first trimester survivors with slow early heart rates proved to have anomalies, as compared to 2.4% (31 of 1281) of cases with normal early heart rates (p < 0.05, Fisher's exact test). In conclusion, a pregnancy in which the embryo has a slow heart rate at or before 7.0 weeks' gestation and which continues beyond the first trimester has a high likelihood (> 90%) of resulting in a liveborn neonate without congenital anomalies. Embryos with slow early heart rates do, however, have a greater risk of having anomalies than embryos with normal early heart rates.

Frequency and nature of structural anomalies in fetuses with single umbilical arteries.

Published studies differ concerning the rate of anomalies occurring in the presence of a single umbilical artery and the significance of the single umbilical artery as an isolated sonographic finding. We assessed the frequency, nature, and sonographic detection of structural anomalies in fetuses with a single umbilical artery. We identified all cases in which prenatal sonography diagnosed a single umbilical artery. Cases were excluded if postnatal physical or pathologic examination demonstrated a three-vessel cord, yielding a study population of 167 cases. For each case, we recorded the gestational age at diagnosis of single umbilical artery and the findings of the sonographic fetal anatomic survey. We recorded postnatal clinical and pathologic information when available. Gestational age at time of diagnosis ranged from 16.8 to 41.1 weeks (mean, 29.2 +/- 6.5 weeks). Twenty of the 167 fetuses (12%) were twins, and the remainder were singletons. Among 118 cases with postnatal information, 37 (31%) had structural abnormalities, often involving multiple organs. The most common organ systems involved were the heart (19 cases) and the gastrointestinal (14 cases) and central nervous systems (nine cases). Five of the anomalous fetuses had abnormal karyotypes. The sonographic survey was abnormal in 31 of the 37 anomalous fetuses (84%). Among 85 cases with apparently isolated single umbilical artery at sonography and known fetal outcome, six (7%) proved to be anomalous at birth. We had two sonographic false-positive results (mild hydronephrosis, suspected skeletal dysplasia). In summary, approximately one third of fetuses with single umbilical artery have structural anomalies, most often cardiac. Even when the single umbilical artery is an apparently isolated sonographic finding, the likelihood that the neonate will prove to have structural anomalies is considerable (7% in our series).

Benign and malignant ovarian masses: selection of the most discriminating gray-scale and Doppler sonographic features.

PURPOSE: To determine the gray-scale and Doppler sonographic features that best enable discrimination between malignant and benign ovarian masses and develop a scoring system for accurate diagnosis with these features. MATERIALS AND METHODS: Gray-scale and Doppler sonographic features of 211 adnexal masses were correlated with the final diagnosis; the most discriminating features for malignancy were selected with stepwise logistic regression. RESULTS: Twenty-eight masses were malignant and 183 benign. All masses with a markedly hyperechoic solid component or no solid component were benign. For masses with a nonhyperechoic solid component, additional features that allowed statistically significant discrimination of benignity from malignancy were, in decreasing order of importance, (a) location of flow at conventional color Doppler imaging, (b) amount of free intraperitoneal fluid, and (c) presence and thickness of septations. A scoring formula that made use of values based on the logistic regression equation had an area under the receiver operating characteristic curve of 0.98 +/- 0.01. The cutoff score with the highest accuracy had a sensitivity of 93% and specificity of 93%. CONCLUSION: A solid component is the most statistically significant predictor of a malignant ovarian mass. A multiparameter scoring system that uses three gray-scale and one Doppler feature, developed by means of stepwise logistic regression, has high sensitivity and specificity for predicting malignancy.

Multifetal pregnancy reduction of both fetuses of a monochorionic pair by intrathoracic potassium chloride injection of one fetus.

The purpose of this study was to determine if a monochorionic pair of fetuses in a higher-order multiple gestation can be reduced by injecting only one fetus with potassium chloride. Three quadruplet and two quintuplet gestations, each with a monochorionic pair of fetuses, were referred for pregnancy reduction. In each case, reduction was performed by injecting one of the monochorionic pair with potassium chloride. Patients returned for a follow-up sonogram within 1 week of the procedure. The reductions were performed at an average 12.1 weeks' gestation, with a range of 10.7 to 14.0 weeks. Follow-up scans 4 to 7 days after the procedure showed that both monochorionic fetuses were dead and all other fetuses were alive. One quintuplet pregnancy underwent a second reduction procedure to twins. One quintuplet and two quadruplet pregnancies that were reduced to twins resulted in the birth of live twins between 30.8 weeks and 36.8 weeks' gestations. The third quadruplet pregnancy reduced to twins is still ongoing; the mother is pregnant with twins at 20 weeks' gestation. The quintuplet pregnancy reduced to triplets resulted in delivery of live triplets at 24.1 weeks' gestation, but two of the neonates died in the first few days of life. Reduction of both fetuses of a monochorionic pair in a higher-order multiple gestation can be accomplished by intrathoracic injection of potassium chloride into only one of the pair.

Sonographic evaluation of the placental cord insertion site.

OBJECTIVE: Velamentous and marginal umbilical cords are uncommon abnormalities of placental cord insertion that can entail significant fetal risk. We undertook this investigation to assess the ability of prenatal sonography to reveal abnormal insertions of the umbilical cord into the placenta. SUBJECTS AND METHODS: Forty-six patients had both prenatal sonographic evaluation of the placental cord insertion site and postnatal pathologic examination. Distance from the insertion site to the nearest placental edge was categorized by sonography and pathology as normal if greater than 1 cm and abnormal if less than or equal to 1 cm. Sonographic and pathologic findings were compared. RESULTS: Thirty-eight singleton and eight twin pregnancies, for a total of 54 cord insertions, were studied. Of the 43 sonographically normal insertions, 38 had normal pathologic findings, and the remaining five insertions had abnormal pathologic findings (all marginal cord insertions). All 11 insertions that showed abnormality on sonography were abnormal on pathologic examination (seven marginal and four velamentous insertions). Sonography was able to reveal a difference between the two types of abnormal insertions in only a single patient, in whom the cord insertion changed from marginal to velamentous during a 7-week interval. Sonography had an overall sensitivity of 69% (11/16), a specificity of 100% (38/38), and an accuracy of 91% (49/54) for revealing abnormal placental cord insertion sites. CONCLUSION: Targeted sonographic examination of the placental site of umbilical cord insertion will reveal abnormal placental cord insertions, although distinguishing the specific type of abnormal insertion may require the use of color Doppler imaging.

"Appearing twin": undercounting of multiple gestations on early first trimester sonograms.

An important role of first trimester sonography is to determine whether a pregnancy is a singleton, twin, or higher order multiple gestation. We assessed how frequently sonography at 5.0-5.9 weeks undercounts multiple gestations. We identified all pregnancies at our institution since 1988 in which (1) an initial sonogram obtained at 5.0-5.9 weeks demonstrated at least a singleton intrauterine pregnancy and (2) a subsequent sonogram at 6.0 weeks or beyond demonstrated a living multiple gestation. Twenty-four (11%) of 213 dichorionic twin gestations were initially undercounted as singletons, as were six (86%) of seven monochorionic twin gestations. Among 105 higher order multiples, 17 (16%) were undercounted initially. All but one of the undercounted cases were scanned transvaginally. Undercounting occurred in both natural and assisted conceptions, and it occurred more frequently on sonograms obtained at 5.0-5.4 weeks than at 5.5-5.9 weeks (P = 0.02, Fisher's exact test). Prognosis for undercounted multiple gestations was similar to that of correctly counted ones with respect to several measures of pregnancy outcome, including the likelihood that all fetuses would be delivered liveborn, gestational age at birth, and birth weight (P > 0.20, all comparisons). In conclusion, transvaginal sonography at 5.0-5.9 weeks frequently undercounts multiple gestations. Initially undercounted multiple gestations and those correctly counted have similar pregnancy outcomes.

Placental implantation on the amniotic sheet: effect on pregnancy outcome.

PURPOSE: To assess pregnancy outcome in patients with amniotic sheets and to determine whether outcome is affected by placental implantation on the amniotic sheet. MATERIALS AND METHODS: Sonograms obtained during the 2nd and 3rd trimesters were reviewed in 157 patients with amniotic sheets to confirm the presence of an amniotic sheet and to determine the relationship of the placenta to the amniotic sheet. The cesarean section rate, gestational age at birth, birth weight, birth weight percentile, and Apgar score 1 minute after birth were recorded in patients in whom the postnatal follow-up data were available. Data were compared with overall data obtained at the authors' institution during the same period. RESULTS: The placenta appeared implanted on the amniotic sheet in 41 (26.1%) of the 157 patients. In the 120 patients with amniotic sheets and follow-up data, the cesarean section rate was 32.5% compared with 21.5% overall. The mean gestational age at birth was slightly lower than that overall (38.2 vs 39.0 weeks, P < .001), but the birth weight percentile was similar (48.6% vs 50.0%, P = .58). No statistically significant differences were found in postnatal follow-up data between pregnancies with placental implantation on and in those without implantation on the amniotic sheet. CONCLUSION: Pregnancy outcome is similar in patients with and in those without placental implantation on the amniotic sheet.

Outcome of pregnancies in women with uterine duplication anomalies.

PURPOSE: This study was conducted to compare pregnancy outcomes in women with uterine duplication anomalies with outcomes in women with normal uteri. METHODS: We studied 22 women with uterine duplication anomalies in whom first-trimester sonography demonstrated a live fetus and compared pregnancy outcomes in these patients with outcomes in 66 women with normal-appearing uteri (controls). The 2 groups were matched for gestational age at the time of first-trimester sonography. RESULTS: Uterine duplication anomalies were associated with a higher miscarriage rate than were normal-appearing uteri (23% versus 6%, p < 0.05, Fisher's exact test). Deliveries resulting in liveborn infants occurred earlier in women with anomalous uteri. The mean gestational age at delivery was 37.0 weeks for women with duplication anomalies versus 38.8 weeks for controls (p < 0.05, Student's t-test), and a higher percentage of duplication anomaly patients delivered before 34 weeks' gestation (29% versus 3%, p < 0.01, Fisher's exact test). Neonates born from anomalous uteri had lower mean birth-weight percentiles than did neonates in the control group (51st versus 68th percentile, p < 0.05, t-test). There was no difference in Apgar scores between the 2 groups at 1 and 5 minutes. CONCLUSIONS: Women with duplication anomalies of the uterus have a higher miscarriage rate, deliver earlier, and have infants with lower birth-weight percentiles than do women with normal-appearing uteri.

Clinical significance of isolated enlargement of the cisterna magna (> 10 mm) on prenatal sonography.

Enlargement of the cisterna magna has been reported to be associated with aneuploidy. In prior studies of cisterna magna enlargement, however, those fetuses with abnormal chromosomes have had other sonographic abnormalities in addition to a large cisterna magna. Our goal was to assess the clinical significance of the isolated finding of a cisterna magna measuring more than 10 mm in anteroposterior dimension on a prenatal sonogram. We retrieved all prenatal sonograms performed at our institution between 1989 and 1996 in which an enlarged cisterna magna was the only sonographic abnormality. Cases were included in our study if the cisterna magna measured more than 10 mm in the appropriate plane and the fetal survey was otherwise normal, including normal cerebellar size and morphology. Pregnancy outcome and postnatal follow-up were obtained in each case. Fifteen cases comprised our study population. In all 15 fetuses, the enlarged cisterna magna was first seen in the third trimester (gestational age range, 26 to 37 weeks). The cisterna magna ranged from 11 to 19 mm in size (mean, 12.9 mm). All 15 pregnancies resulted in phenotypically normal liveborn infants. All the mother and infants had short hospital stays (1 to 4 days), and the infants were normal at discharge. Longer follow-up was available in eight cases (range, 2 to 69 months), and all eight of these infants were normal. Our results suggest that isolated enlargement of the cisterna magna to more than 10 mm is associated with normal pregnancy and neonatal outcome.